The Roman Fasti

A Roman calendar was not a neutral grid of dates the way a modern wall calendar is. Every day carried a legal and religious classification, dies fastus, on which a praetor could hear a case and public business could be transacted, or dies nefastus, reserved for the gods and closed to civic business by the same stroke that made it a day the state could not touch. Feriae, the fixed festival days of the state cult, sat on top of that basic division, each with its own sacrifices and rites specified by the pontifical calendar the priestly college maintained, from Saturnalia in December, with its temporary inversion of social roles between master and slave, to the winter solstice festival for the unconquered sun, Dies Natalis Solis Invicti, that later Christian tradition situates near its own December feast.

What survives today is not a single master fasti from the city of Rome but multiple versions inscribed on stone in towns across Italy, at different dates and reflecting some local variation in which festivals a given community chose to mark, which together make the Roman religious calendar one of the most thoroughly documented in the ancient world despite the absence of one complete official copy.

Before Julius Caesar's reform, the Roman calendar was lunar in origin and needed an intercalary month inserted periodically to keep pace with the solar year, and the decision of when and whether to intercalate belonged to the pontifices, the priestly college responsible for the calendar's upkeep. That discretion was abused for ordinary political advantage: lengthening a friendly magistrate's term or shortening a rival's simply by deciding whether the current year would run long, and by the first century BCE the civil calendar had drifted badly out of alignment with the actual seasons it was meant to track.

Caesar's reform of 46 BCE, carried out with the astronomer Sosigenes, fixed the year at 365 days with a leap day added every fourth year, removing the discretionary intercalation that had made the calendar a political instrument and giving the fasti a stable solar frame that has run, with the later Gregorian correction to its leap rule, into the calendar most of the world uses today. The Julian Calendar entry in this atlas covers that civil reform itself; the fasti covers the religious classification of days and the festival cycle that reform stabilised rather than replaced.